In an attempt at reducing a window surface thermal load caused by sunlight in cooling a room, or at improving the room heating efficiency by heat recovery of air warmed by sunlight; or, to let a window exert its function as an insulated window and a radiation window; there are ideas of configuring openings such as windows with a double-glazed glass having necessary components. Patent literatures 1 and 2 are propositions for this kind of ideas.
Patent literature 3 describes an art as follows: An inner sash that works as an inner glass wall is installed in the indoor side of an existing mullion provided inside the existing glass curtain wall for supporting it. Thereby, the art allows a double glass skin being formed by a retrofit installation work accessing only from the indoor side to improve the room-cooling efficiency.
Therefore, the invention described in Patent literature 3 is able to form a double skin glass by arranging an inner sash inside an existing glass curtain wall by a retrofit installation. The invention however uses an inner sash (literally a frame). Therefore a plate glass without supporting frame cannot be applicable. A large sized plate glass to be used for a big opening may be reinforced by a frame against insufficiencies of its rigidity, but such frame itself may cause a problem of unsightliness in a viewpoint of design.